The present invention relates to a polishing apparatus for polishing a surface of a workpiece, such as a semiconductor wafer, to a high degree of fineness.
In a semiconductor device manufacturing process, a polishing apparatus is used to polish surfaces of semiconductor wafers. However, during polishing, particles become detached from the wafer and scattered around the polishing apparatus, and hence it has not been possible to use a conventional polishing apparatus in a clean room environment. In addition, in a conventional system, the wafer after polishing is placed in a mobile water tank for transportation to a cleaning apparatus, which is inefficient in terms of both the time and space required to complete a polishing and cleaning operation.
To solve the above-mentioned problems, a so-called dry-in/dry-out system has been developed in which polishing and cleaning processes are carried out in an apparatus enclosed within a housing. In the dry-in/dryout system, a semiconductor wafer is loaded into the apparatus in a dry state, and is unloaded in a dry state after polishing and cleaning.
Aside from the development of the dry-in/dry-out system, a polishing apparatus per se has been modified such that it is able to be used in a clean room. Further, improvements in the processing efficiencies of a polishing apparatus and a cleaning apparatus have enabled their installation in a space equal to or smaller than that required for the installation of a dry-in/dry-out system. However, there remains a difficulty in the automation of the wafer transportation means incorporating a mobile water tank.
An object of the present invention is to provide a polishing apparatus which is applicable to the above-described dry-in/dry-out polishing system, by use of which the efficiency of polishing workpieces such as semiconductors can be increased both in terms of the time required and space utilized.
According to the present invention, there is provided a polishing apparatus comprising a polishing table having a polishing surface, a substrate carrier having an axis about which the substrate carrier is rotatable. The substrate carrier includes a plurality of substrate holders positioned around a circle about the axis of the substrate carrier and spaced apart from each other at equal angular distances, with each of the carriers being adapted to hold a substrate and bring It into contact with the polishing surface. The apparatus further comprises a substrate loading device laterally spaced apart from the polishing table, in which device a substrate is picked up by one of the substrate holders which is positioned at the substrate loading device, and a substrate unloading device laterally spaced apart from the polishing table, in which device one of the substrate holders which is positioned at the substrate unloading device releases a wafer onto the unloading device. The substrate carrier is indexably rotated about the stated axis in such a manner that one of the substrate holders is selectively positioned at the loading device, while another substrate holder is positioned at the unloading device and at least one of the other substrate holders is positioned over the polishing surface.
In the present invention, polishing, loading and unloading of substrates with respect to the polishing table are simultaneously effected. Therefore, the number of substrates processed per unit time (throughput) can be remarkably increased.
The polishing apparatus may comprise a liquid spray nozzle for supplying a liquid spray to the substrate held by the substrate holder positioned at the loading device and/or the unloading device. In the polishing apparatus, when polishing is conducted for a prolonged period of time or when the apparatus is stopped for a long time due to an emergency stop, it is possible to prevent the substrate from becoming dry thus avoiding the problem of dust, by spraying a liquid over the substrate in a standby condition.
The polishing apparatus may comprise three of the substrate holders, and the substrate carrier may be indexably rotated about the axis of the polishing table in such a manner that one of the substrate holders is selectively positioned at the loading device, while another substrate holder is positioned at the unloading device and the other substrate holder is positioned over the polishing surface.
The polishing apparatus may comprises four of the substrate holders, and the substrate carrier is indexably rotated about the stated axis in such a manner that one of the substrate holders is selectively positioned at the loading device, while another substrate holder is positioned at the unloading device and the other two substrate holders are positioned over the polishing surface. In the apparatus, polishing is effected twice and, as a result, it becomes possible to increase a throughput, while securing a sufficient polishing time. The two polishing positions are secured on a single polishing table (turntable), to thereby reduce the size of the apparatus.